1. Field of the Invention
The present invention relates generally to a steering apparatus for four-wheeled vehicles. More particularly, the invention relates to a steering apparatus for changing a ratio between turning angles of front and rear wheels in response to speeds of the vehicle.
2. Description of Relevant Art
Vehicles of the four-wheeled type are generally steered by turning the two front wheels with respect to the longitudinal axis of the vehicle. As the front wheels start to turn while the vehicle is running, an angle of slippage is developed at the front wheels, thereby producing a cornering force which causes the vehicle body to move transversely and to yaw about the center of gravity of the vehicle body.
An angle of slippage is generated at the rear wheels only after the vehicle body has started being displaced due to the yawing movement thereof. Accordingly, a cornering force acts on the rear wheels a short interval of time after the cornering force has acted on the front wheels of the vehicle. In other words, there is a short time lag before the resultant combined cornering forces on the front and rear wheels reaches a value which the driver of the vehicle is expecting. Such time lag causes driving of a four-wheeled vehicle to be more difficult.
While the four-wheeled vehicle is steered to move around, the wheels are subjected to lateral slippage, so that the longitudinal axis or orientation of the vehicle tends to be out of alignment with a tangential line on an arcuate path upon which the vehicle moves. This presents another difficulty in driving a four-wheeled vehicle.
Accordingly, the driver of a four-wheeled vehicle is required to take into consideration a time lag between the turning of the front and rear wheels, and an angular difference between the tangential line on the arc which the vehicle is to sweep, and the longitudinal axis of the vehicle. For proper and safe driving of four-wheeled vehicles, therefore, the driver must have considerable driving experience.
The present invention overcomes the above-described problems by providing a steering apparatus for four-wheeled vehicles wherein a ratio between turning angles of front and rear wheels of the vehicle is variable with vehicle speeds, and the vehicle is provided with an improved steering responsiveness.